A family of neurite outgrowth-promoting factors has been characterized and each factor has been shown to be a complex of laminin and a heparan sulfate proteoglycan, in which laminin funcitons as a potent inducer of neurite outgrowth in an in vitro assay. The characterization of these factors will be completed, using electron microscopy. Possible reasons why laminin and neurite-outgrowth-promoting factors differ in their sensitivities to antibodies will be studied. The sites on laminin that are required for its actions on neurons will be identified and characterized. Efforts will be made to identify the receptors on neurons that mediate the actions of laminin. In particular, the role of a purified neuronal cell surface heparan sulfate proteoglycan that has been shown to bind laminin will be studied. Using a responsive cell line, PC12 cells primed by growth with NGF, some of the intreacellular changes caused by laminin will be identified and compared to those induced by Nerve Growth Factor. Antibodies to laminin, laminin-heparan sulfate proteoglycan complexes, and neuronal receptors will be used to characterize the role of neurite outgrowth-promoting-factors in mediating neuronal axon outgrowth on substrates and cells that growth cones encounter in vitro. Injections of antibodies into chick will be used to identify possible roles for LN in developing and in regenerating nerves.